This invention generally relates to plastic bottles suitable for retention of fluids under pressure, including carbonated beverages or the like. In particular, the present invention relates to a footed plastic bottle having an integral base that provides a stable support for the plastic bottle on level surfaces.
Carbonated beverages such as soft drinks are commonly packaged in lightweight, flexible, plastic containers. Because of their reduced rigidity as compared to glass containers, early efforts to manufacture plastic containers typically involved construction of hemispherical bases. A hemispherical base design can withstand high internal pressure and shock induced external pressures by evenly distributing the pressure induced stresses. A hemispherical base design maximizes the volume contained by a given amount of plastic material, and allows relatively thin plastic containers to withstand internal pressures as high as 100 p.s.i. without failure.
However, hemispherical base containers are not without problems. Hemispherical base containers require a separate base cup to support the plastic container in an upright position. Manufacture and attachment of this separate base cup is not always cost-effective, in part because of increased manufacturing costs and because it requires incorporation of failure prone base cup attachment production steps.
To avoid these problems, plastic container manufacturers have produced a variety of one piece plastic containers having a non-hemispherical bases modified to support the container. For example, "champagne" type bases having a complete annular ring capable of resting upon a level surface have been disclosed in U.S. Pat. Nos. 3,722,726; 4,108,324; 4,247,012; and 4,249,666. Although such one-piece champagne type plastic bottles are stable without a base cup, they still require significant increase in plastic resin to form the base, and even with the increased plastic resin are still prone to drop impact failure as compared to hemispherical bottles.
An alternative to both hemispherical and champagne type bases has been developed. Commonly known as a "looted" container, this type of base is disclosed, for example, in U.S. Pat. Nos. 3,598,270; 4,294,366; 4,368,825; 4,865,206; and 4,867,323. Footed containers typically have multiple feet that bulge or protrude outward from an otherwise generally hemispherical base. Manufacture of such footed containers can be difficult, since uneven distribution of the plastic resin in the base can cause uneven projection of the feet when the container is filled with a carbonated liquid, resulting in a "rocker bottom" that allows the container to wobble. Further, provision of the feet can unduly increase stress concentration in the feet, again resulting in increased drop impact failure. Additionally, when such a container is filled with a carbonated liquid, the axial portion of the container bottom can creep or grow downwardly to contact the supporting surface or even protrude below the level of the bottom of the feet again resulting in a "rocker bottom" that allows the container to wobble.